Two more schools have been closed and a fifth person has fallen seriously ill from swine flu after health authorities reported another large jump in confirmed cases.

Health officials said there were 55 new cases across the UK today, taking the running total so far to 459, including a woman aged 44 now in a hospital high dependency unit in Scotland.

One of the largest clusters of case so far – surrounding the seaside town of Dunoon in Argyll, where one primary school has already been closed and around 70 case reported – appears to have spread.

There were 21 new cases in the area, including children at two primary schools in Cowal near Dunoon. The two schools were closed today, with more than 200 children sent home and given anti-viral drugs as a precaution.

These mild cases are linked to a primary school trip involving several local schools: the 70 pupils and 20 staff at the event are being given Tamiflu. In addition, 230 third-year pupils in Paisley have been sent home.

The Scottish health secretary, Nicola Sturgeon, said the 37-year-old Sikh man from the south side of Glasgow who became the first Briton to fall critically ill was now recovering. He had been moved out of intensive care.

Three people remain critically ill in an isolation ward at the Royal Alexandra hospital in Glasgow, where the 44-year-old woman is now in the high dependency unit.

Sturgeon said many further cases were expected, and underlined her warning earlier this week that the main strategy of containing each virus outbreak may need to change.

The government's emergency committee Cobra is considering whether to stop trying to prevent the virus spreading, and just treat cases as they emerge. Sturgeon said health officials were doing "all we can to slow the spread of the virus".